Lead fixation accessory, lead stabilization tool, and related procedures

ABSTRACT

A lead fixation accessory configured to be positioned over a skull hole and to transition between an opened state and a closed state during a lead implant procedure protects against lead migration by providing a mechanism for securing the lead in place at the skull hole while a style(is removed from the lead. The lead fixation accessory remains in place after the implant procedure to provide chronic lead stability. A lead stabilization tool configured to access and grip a lead through a slotted cannula during the lead implant procedure also protects against lead migration by providing a mechanism for securing the lead in place at a point where the lead exits the skull hole while the slotted cannula is removed from the skull hole and peeled away from the lead.

BACKGROUND Field

The present disclosure relates generally to apparatuses and methods usedwhen implanting a medical device in a patient, and more particularly, toaccessories, tools, and methods for using the same that minimize thedegree to which the distal end of an implanted brain lead will bedislodged from its target in or on brain tissue once it has been locatedthere, due to manipulation of the lead in subsequent steps in theimplantation procedure.

Background

Some diagnostic or interventional medical procedures require implantingone or more leads through a hole in a patient's cranium. Once thesurgeon places a lead so that the distal end is at a desired location,the surgeon wants the lead to stay there for whatever ultimate medicalpurpose the lead has, for example, to monitor physiological parametersfrom a patient or to deliver a therapy to the patient. Usually, however,there are steps subsequent to placing the lead that are necessary tocomplete the surgical procedure, and some of these may cause inadvertentdisplacement of the lead away from the desired location, which may notbe corrected easily or efficiently.

Generally, leads may be provided with electrodes configured to senseinformation from the brain or to deliver a form of stimulation to thebrain intended to modulate neural activity, such as electricalstimulation. The sensing and/or stimulation may occur at a distal end ofthe lead, for example, through electrodes exposed to brain tissue at adistal end, wherein the signals are communicated through conductorsdisposed in the lead body extending to a lead proximal end. Connectionsavailable at the lead proximal end allow the lead to be connected toanother medical device, implanted or external, that processes the sensedsignals and/or generates the form of stimulation.

For example, in the responsive neurostimulation system manufacturedunder the tradename INNS SYSTEM by NeuroPace, Inc., the proximal ends ofone or more implanted brain leads can be connected to another implantedmedical device, namely a neurostimulator that is seated in a tray orferrule in a craniectomy in the patient's skull. In another example, theleads may be implanted in a patient so that an intracranial monitoringprocedure can be undertaken for a period (e.g., several days or a coupleof weeks), with the proximal ends of the implanted leads being connectedto external equipment monitoring the patient's brain activity, such asto identify a focus or the foci of epileptiform activity in the patient.

There are multiple types of brain leads currently available. Inapplications where the leads are being used to sense or stimulate braintissue at or near the focus of undesirable epileptiform activity, thereis a depth lead (also sometimes referred to as a “deep brain lead” or asa “stereotactic depth lead”, because this lead type is often implantedusing stereotaxy, a three-dimensional localization and placementprocedure) and a cortical strip lead (also known simply as a “corticallead” or as a “subdural lead”, because this lead type is usuallyimplanted underneath the dura mater).

A depth lead is implanted so that the distal end is located in the braintissue, in or adjacent a structure that is deemed to be associated withthe generation of the undesirable activity. A cortical strip lead isimplanted so that the distal end lays on a surface of the brain at oradjacent brain tissue that is believed to comprise an epileptic focus.The intended location of the distal end of the brain lead in or on thebrain is referred to hereinafter as the “target”.

A lead manufacturer may make different lead types in one or morestandard lengths, rather than in lengths customized for a particularapplication in a particular patient. In addition, the depth lead typemay be intended to be implanted using stereotactic equipment or someother tool that requires some length in excess of that which is neededto extend from the cranium and the connection to another medical deviceand the target (e.g., so that the lead is long enough to extend throughthe distance required when using a stereotactic frame mounted to thepatient). For at least the reason that a lead may be manufactured tohave more length than is necessary to traverse the distance between theproximal connection to another implant or external equipment and thetarget, brain leads are often manufactured to be quite flexible. Thatis, if the lead is flexible, excess length can be coiled or folded atthe surface of the skull before the scalp is replaced. Further,flexibility may be considered a better alternative than a stiff leadwhen the lead is to remain in place in or on a surface of the brainchronically, as opposed to acutely, such as to minimize tissue damageand to optimize the integrity or resolution of signals. Brain leadsmanufactured and sold with the RNS SYSTEM, for example, have aflexibility on par with that of a piece of cooked spaghetti.

When implanting a lead in the brain tissue, though, its relativeflexibility can present challenges when delivering the distal end to thetarget. Accordingly, a brain lead is often provided with an inner lumenthrough which a removable stiffener, such as a stylet, can be disposed.The stylet lends stability to the lead while the distal end is routed tothe target, and is then removed when the lead has been positioned whereit is intended to remain, either acutely or chronically. It isundesirable, however, if the act of withdrawing the stylet causes thedistal end to move away from the target.

Equipment or tools used in implanting a brain lead can alsounintentionally cause the distal end of a brain lead to move away fromthe target in procedural steps undertaken subsequent to placing thelead. For example, a slotted cannula is often employed in implantingleads stereotactically, in which a hole is formed in the patient's skullat a location calculated to allow an appropriate trajectory of a lead todeep brain target. In one example of such a procedure, a frame isattached to the patient, and a guide tube is oriented to achieve thedesired trajectory relative to the skull hole. A cannula is insertedthrough the guide tube, such that its range of motion is constrained bythe guide tube. The cannula may be provided with a removable roddisposed in an inner lumen thereof. The cannula is advanced through theskull hole towards the target. The inner rod in the cannula preventstissue from backing up into the cannula while it is advanced.

When the cannula has been advanced to or approximate the target, theinner rod is removed and a depth lead inserted into the cannula lumen.The surgeon then advances the depth lead to the target. (Sometimes thedepth lead is marked in advance at a proximal location, for example,with a stop gauge, to provide feedback to the surgeon when the targethas been reached.) Once the distal end of the lead reaches the target,the cannula must be withdrawn from the brain and the lead must beextracted from the cannula, so the stereotactic equipment can beremoved. A cannula is often provided with a longitudinally-extendingslot with a width wide enough to accommodate the diameter of the leadbody for this purpose, i.e., so that the lead can be stripped away fromthe cannula using the slot, rather than having to retract the cannulaover the lead body. This allows the lead to be manufactured withsomewhat less excess lead length than if the lead had to be long enoughto retract the cannula over the very proximal end of the lead. As is thecase with withdrawing a stylet, it is undesirable if the act ofdisengaging the lead body from a cannula (or other apparatus used forstereotaxy) causes the distal end of the brain lead to move away fromthe target.

A hole in the skull is often formed with some standard diameter, owingto the drills typically available in the operating room to create it.When an air drill is used to create a hole in the skull with a diameterof 5 mm or greater, the skull hole is often referred to as a “burrhole.” Surgeons create standard-sized burr holes, because there aresurgical accessories intended for use with burr holes that are intendedfor use with certain burr hole diameters, such as 14 mm. However, thediameter of a brain lead may be much smaller than that of a burr hole,because 14 mm is on the order of ten times greater than the diameter ofthe lead to be implanted. For example, some brain leads manufactured byNeuroPace, Inc. have a diameter of only 1.27 mm. Therefore, in somecases a surgeon may choose to use a smaller diameter hole through whichto implant a lead. For example, a surgeon may choose to use a hand-heldtwist drill to create a hole with a diameter on the order of less than 5mm (depending on the diameter of the twist drill bit: a common oneresults in a 3.2 mm diameter hole). A skull hole formed using a twistdrill is sometimes referred to as a “twist drill hole”.

In view of the foregoing, it would be beneficial to provide accessoriesand tools that reduce the likelihood that the distal end of a brain leadwill be dislodged after it has been implanted at a target, as aconsequence either of surgical steps or post-surgical factors, such as apatient fiddling with the lead or the skull hole through the scalp.Embodiments of a lead fixation accessory, a lead stabilization tool, andmethod of using them disclosed herein address these needs and others.

SUMMARY

Disclosed herein are apparatuses and methods for discouraging movementof a lead implanted through a skull hole once the surgeon has placed thedistal end of the lead at a desired target. A versatile lead fixationaccessory can be used with a variety of diameters of skull hole, and canbe affixed to the skull before or after a lead has been implantedthrough a skull hole. The simple but effective design allows the leadbody to be chronically secured at or near the skull hole, even while anystiffening member (such as a stylet) remains in place in the lead in theimplanted lead, so that manipulating the lead to remove the stylet isless likely to dislodge the lead distal end from the target.

A lead fixation accessory according to embodiments includes a first armhaving opposed ends separated by a middle region and a second arm havingopposed ends separated by a middle region. A coupling mechanism couplesrespective first ends of the first arm and the second arm together sothat the lead fixation accessory can transition between an open state orposition and a closed state or position. While in an open position, therespective second ends of the first and second arms are displaced fromeach other. In a closed position, the respective second ends of thefirst and second arms are engaged, and the respective middle regions ofthe first and second arms form at least one opening sized to secure alead in place near a hole formed in a skull.

In one configuration, the arms are separate components that are coupledtogether during placement of the lead fixation accessory. To this end,the coupling mechanism is an attachment mechanism, e.g., a bone screw,that couples the first and second arms together by attaching the firstends of the arms to a surface of the skull in a way that allows forrotational movement of the arms relative to each other. In otherconfigurations, the lead fixation accessory is a fully assembled device.In this case, the coupling mechanism may be a hinge assembly thatcouples the first and second arms together in a way that allows forrotational movement of the first arm and the second arm prior toplacement on the skull. The hinge assembly may include an opening thatreceives an attachment mechanism for attaching the lead fixationaccessory to the skull. Alternatively, an opening through one or more ofthe arms may receive an attachment mechanism. In either configuration,once the lead fixation accessory is secured to the skull, the accessorymay then be closed by rotating one of the arms until the second ends ofthe arms engage, after which the lead fixation accessory may be furthersecured to the skull using an additional attachment mechanism.

The one or more openings of the lead fixation accessory that secure alead are characterized by a geometry or cutout shape formed by themiddle regions of the first and second arms. For example, if the edgesof the middle regions that face each other when the accessory is closedare linear, the geometry of the opening defined by facing edges would bea rectangle. If one of the facing edges includes a semicircular cutoutand the other is linear, the geometry of the opening would be asemicircle. Numerous other opening shapes are possible. Furthermore,several separate openings—each for securing a separate lead—may beformed by an edge that includes multiple cutouts and a linear edge. Inall cases, the cutout shape is characterized by a dimension that ensuresthat the middle regions of the accessory apply a force to the leadsufficient to hold the lead in place. For example, a circular openingwould have a diameter slightly less than the diameter of the lead body,so that when the accessory is closed around the lead body and secured tothe skull, the lead body is affixed to the accessory.

A lead stabilization tool according to embodiments is configured to holda lead in place near a hole in a skull during a lead implant procedure.The lead stabilization tool includes a housing, an extension member atleast partially located in the housing, a grip structure, and anoperating mechanism configured to transition the lead stabilization toolbetween an extended state and an at least partially retracted state. Inan extended state, the grip structure is located distal a nose of thehousing so that it can be positioned through a slotted wall of a cannulaand manipulated to at least partially encircle the lead. In a partiallyretracted state, the grip structure is located relative to the nose toapply a force to the lead to thereby hold the lead in place.

Transitioning of the tool between an extended state and a retractedstate may be implemented through displacement of the extension memberalong a longitudinal axis of the housing. To this end, the operatingmechanism may include a push button coupled to the extension memberthrough a biasing mechanism that translates a force applied to the pushbutton in a direction perpendicular to the longitudinal axis to a forceapplied to the extension member in the direction of the longitudinalaxis. In another variation, the operating mechanism may include arotational thumb wheel coupled to the extension member by a threadedengagement that translates rotational force applied to the thumb wheelto a force applied to the extension member in the direction of thelongitudinal axis. IN yet another variation, the operating mechanism mayinclude a slide button coupled to the extension member by a fixedmechanical engagement that transfers force applied to the slide buttonto the extension member in the direction of the longitudinal axis.

It is understood that other aspects of accessories, tools, and methodsfor using the same will become readily apparent to those skilled in theart from the following detailed description, wherein various aspects ofapparatuses and methods are shown and described by way of illustration.As will be realized, these aspects may be implemented in other anddifferent forms. Accordingly, the drawings and detailed description areto be regarded as illustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of apparatuses and methods will now be presented in thedetailed description by way of example, and not by way of limitation,with reference to the accompanying drawings, wherein:

FIG. 1A is a schematic of a patient's cranium showing implantedcomponents of a neurostimulation system, including leads and aneurostimulator, and related surgical accessories, including a burr holecover and a lead fixation plate.

FIG. 1B and 1C are illustrations of known burr hole covers.

FIG. 1D is an illustration of a known lead fixation plate.

FIG. 2 is an illustration of some components of stereotactic equipmentthat may be used in a standard stereotactic procedure with a frame toimplant a depth lead in a patient's brain.

FIG. 3 is an illustration of a cannula (with a depth lead insertedtherein) that may be used during a procedure for implanting a depthlead.

FIG. 4A is a perspective view of a lead fixation accessory according toembodiments in an open position.

FIG. 4B is a perspective view of the lead fixation accessory of FIG. 4Ain a closed position.

FIG. 4C is a top view of the lead fixation accessory of FIG. 4B.

FIG. 4D is a front view of the lead fixation accessory of FIG. 4B.

FIG. 4E is a side, end view of the lead fixation accessory of FIG. 4B.

FIG. 4F is a perspective view of the lead fixation accessory of FIG. 4Awith partial cutaways to expose portions of components of the accessory.

FIGS. 4G-4I are illustrations of different mechanisms for couplingcomponents of the lead fixation accessory together to allow for rotationof the components.

FIG. 5A is a top view illustration of a lead stabilization tool in adeactivated or resting state and having an operating mechanism thatincludes a push button.

FIG. 5B is a side view of the lead stabilization tool of FIG. 5A.

FIG. 5C is a detail view of the distal end of the lead stabilizationtool of FIG. 5A.

FIG. 5D is a cross section of the lead stabilization tool of FIG. 5A.

FIG. 5E is a top view of the lead stabilization tool in an extendedstate.

FIG. 5F is a cross section of the lead stabilization tool of FIG. 5E.

FIG. 5G is a top view of the lead stabilization tool in a partiallyretracted state and holding a lead.

FIG. 5H is a side view of the lead stabilization tool of FIG. 5G.

FIG. 5I is a side view illustration of a lead stabilization tool havingan operating mechanism that includes a thumb wheel with a threadedcoupling.

FIG. 5J a perspective view of the thumb wheel component of the leadstabilization tool of FIG. 5I.

FIG. 5K is a cross section of the lead stabilization tool of FIG. 5I.

FIGS. 5L and 5M are side view illustrations of an alternateconfiguration of the operating mechanism of FIG. 5I that includes athumb wheel with cam coupling.

FIGS. 5N and 5O are side view illustrations of a lead stabilization toolhaving an operating mechanism that includes a slide button.

FIGS. 5P-5U are schematic illustrations of grip structures that may beincorporated into a lead stabilization tool.

FIG. 5V is a side view illustration of lead stabilization tool in adeactivated or resting state having dual operating mechanisms, includinga thumb wheel for transitioning the tool between resting, extended, andpartially retracted states, and a slide button for manipulating a gripstructure between linear and curved states.

FIG. 5W is a side view illustration of the lead stabilization tool ofFIG. 5V in an extended state, and showing the grip structure in a linearstate and a curved state.

FIG. 5X is a side view illustration of the lead stabilization tool ofFIG. 5V in a partially retracted state and holding a lead.

FIG. 6 is a flowchart of a method for implanting a depth lead accordingto embodiments.

FIGS. 7A-7R are top-view and side-view schematics of various stages ofthe method of FIG. 6.

FIG. 8 is a schematic view of a patient's cranium showing an implanteddepth lead and an implanted cortical lead, each of which is secured at arespective skull hole by two different lead fixation accessoriesaccording to the embodiments of FIGS. 4A-4F.

FIG. 9A is a top view of a lead fixation accessory according toembodiments in an open position.

FIG. 9B is a top view of the lead fixation accessory of FIG. 9A in aclosed position.

FIG. 9C-9E are top views of different configurations of the leadfixation accessory of FIGS, 9A and 9B.

FIG. 9F is a top view of a lead fixation accessory according toembodiments in an open position.

FIG. 9G is a top view of the lead fixation accessory of FIG. 9F in aclosed position.

FIG. 10A is a schematic illustration of tensile force on a lead in asituation where the lead is firmly affixed at a given point—without astrain relief member.

FIG. 10B is a schematic illustration of tensile force on a lead in asituation where the lead is firmly affixed at a given point—with astrain relief member.

FIG. 11 is a flowchart of a method for implanting a depth lead accordingto embodiments.

FIG. 12A-12D are top-view and side-view schematics of various stages ofthe method of FIG. 11.

DETAILED DESCRIPTION

Disclosed herein in detail are embodiments of a lead fixation accessorythat allow the body of a brain lead to be secured at the surface of apatient's skull while a stiffening element, such as a stylet, remains inplace in a lumen of the lead body. The stiffening element thus can bewithdrawn from the lead after the lead fixation accessory is in place,reducing the likelihood that the act of pulling out the stylet willdisplace the distal end of the implanted lead away from the target.

Also disclosed herein in detail are embodiments of a lead stabilizationtool for use in a procedure to implant a brain lead using a slottedcannula that allow the lead body to be stabilized near the surface ofthe patient's skull while the slotted cannula and the lead body areseparated from each other, which makes it less likely that the act ofseparating the cannula and the lead will cause the lead to pull awayfrom the target than if the lead body had to be stabilized proximally ofthe skull surface, such as at or above the top of the cannula.

The embodiments are described primarily with reference to the medicaldevice being an electrode-bearing lead, as might be used in anapplication for deep brain stimulation or direct brain stimulation suchas the responsive stimulations applications by NeuroPace, Inc. ofMountain View, Calif. It should be appreciated, however, that the leadfixation accessory and the lead stabilization tool may be used with goodresults to secure a segment of a different type of medical device, suchas a catheter or other medical instrument (with a diameter compatiblewith the accessory), relative to a surface of the skull prior to and/orduring use of the medical device in its intended application. Similarly,it should be appreciated that, in some circumstances, embodiments of alead fixation accessory described herein may be used to secure more thanone medical device simultaneously (e.g., two leads) for someapplications.

Overview of Procedures to Implant Brain Leads, Tools, and Devices

For purposes of illustration, procedures to implant a depth lead and acortical strip lead will be described with reference to a responsiveneurostimulation system, in which a surgeon commonly uses both leadtypes.

With reference to FIG. 1A, a neurostimulator 110 and leads 120, 130 of aresponsive neurostimulation system are shown schematically, implanted ina patient. To implant a lead, the surgeon needs access to the brain. Asurgeon may gain access to the brain for purposes of implanting a leadby creating an opening through the skull. A opening may be created bydrilling a hole through the skull, by performing a craniotomy(temporarily removing a bone flap from the skull and replacing the flapafter access to the brain is no longer needed) or by performing acraniectomy (permanently removing a bone flap from the skull). Suchopening may be used exclusively for lead implant purposes, or may beused for another/additional purpose (for example, the surgeon can firstdeliver a lead to a target through an opening formed as part of acraniectomy, then use the same opening to implant another medicaldevice, such as a neurostimulator). The term “skull hole” is used hereinto refer to any category of opening formed in a patient's skull to gainaccess to the subdural spaces and to the brain.

In FIG. 1A, three skull holes have been formed: a burr hole 140 forpurposes of implanting a depth lead 120, a craniotomy 150 for purposesof implanting a cortical strip lead 130, and a craniectomy 160 in whicha tray or ferrule 112 and a neurostimulator 110 are ultimatelyimplanted. More particularly, the surgeon may use an air-powered drillto form an annular burr hole 140 of a diameter between 5-30 mm, with 14mm being a commonly-used diameter, for purposes of implanting a depthlead 120. Using appropriate tools, the surgeon may also perform acraniotomy 150 for purposes of implanting a cortical strip lead 130, andadditionally a craniectomy 160 in which to ultimately situate aneurostimulator at the patient's skull.

In FIG. 1A, a distal portion 122 of the depth lead 120 extends into thepatient's brain tissue from a 14-mm burr hole 140, and a proximalportion 128 extends proximally from the burr hole where it is plugged inat a proximal end 129 to a connector 114 of an implanted neurostimulator110. A distal portion 132 of a cortical strip lead 130 extends from afissure like opening or hole 151 at an edge of the craniotomy 150 onto asurface of the patient's brain, between the brain and the dura mater(not shown), and a proximal portion 138 extends proximally from the holewhere it is plugged in at a proximal end 139 to the connector 114. Theneurostimulator 110 has a strain relief 116 in the location where theproximal ends 129, 139 of the leads connect, to discourage the leadsfrom unintentional disconnection.

A distal end 124 of the depth lead 120 includes a plurality ofelectrodes 126 (three are shown in FIG. 1A), that can be used either forsensing electrographic activity from the brain or for delivering atherapy of electrical stimulation to it in an effort to modulate neuralactivity (e.g., lessen the severity of a seizure). Conductors extendingthe length of the lead body (not shown) and connected at the connector114 to the neurostimulator 110 allow the neurostimulator to process thesensed signals and to generate the stimulation signals. A distal end 134of the cortical strip lead 130 ends in a paddle 136 that, on abrain-facing surface thereof (not shown in FIG. 1A), exposes anotherplurality of electrodes (e.g., four) to the brain surface underneath thedura mater. These electrodes are also in electrical communication withthe neurostimulator 110 via conductors in the cortical strip lead 130and the connection at the connector 114.

In addition to the burr hole 140 or the craniotomy 150 opening 151, alead, especially of the cortical strip lead type, may be implanted usinganother opening in the cranium. More specifically, to implant theneurostimulator 110, the surgeon cuts a craniectomy 160 hole using atemplate that approximates the shape of the neurostimulator. The surgeonfits a tray or “ferrule” 112 into the hole and attaches or otherwisesecures it to the cranium, for example, using bone screws and/or foldingtabs 118 providing on the tray. The surgeon then situates theneurostimulator 110 into the tray 112. However, before placing the tray112, the surgeon can use the craniectomy 160 hole to implant a corticalstrip lead, such as the cortical strip lead 130, and then connect theproximal end thereof to the neurostimulator connector. (FIG. 1A does notshow any lead implanted using the craniectomy 160 in which the tray 112and neurostimulator 110 are situated.)

Both of the implanted leads 120, 130 in FIG. 1A are shown secured withknown lead fixation accessories. The depth lead 120 implanted throughthe burr hole 140 is shown secured with a burr hole cover 144 whichsubstantially fills the 14-mm diameter burr hole except for an aperturetherethrough that permits passage of the lead body. Examples of leadfixation accessories designed for burr holes are illustrated in FIGS. 1Band 1C.

Some burr hole lead fixation devices are designed for use withmechanical parts that need to be actuated in order to achieve fixationof the lead body, and others rely on friction fit or compression tolimit movement of the lead relative to the device. Some require at leastone element of the accessory to be put in place before a procedure toimplant a lead is begun. Some allow fixation only after any stiffeningelement used in implanting the lead has been removed. With reference toFIG. 1B, a burr hole lead fixation accessory manufactured by Medtronic,Inc. under the tradename “STIMLOC” uses several interlocking parts tosecure a lead body. With reference to FIG. 1C, a two-piece burr holecover manufactured by NeuroPace, Inc. relies in part on fitting aportion of the lead body into a groove in base element to reduce thelikelihood that further manipulation of the lead portion extendingproximally of the skull hole (e.g., to connect the lead to an implantedneurostimulator) will translate to movement of the distal end away fromthe target.

In FIG. 1A, the cortical strip lead 130 implanted through the craniotomy150, and having a proximal portion 138 extending from the opening 151 atan edge of the craniotomy 150 onto the surface of the skull is securedat a point on the lead body just proximal of where the lead body extendsout of the hole, with a cranial plate 154. The cranial plate 154 issituated over the lead body and then secured to the surface of the skullon either side of the lead body with bone screws. Because of its shape,the type of cranial plate 154 shown in FIG. 1A is commonly referred toas a “dog bone”. One such plate is shown in FIG. 1D and is manufacturedunder the tradename “MATRIXNEURO” by Synthes CMF. The cranial plate 154compresses the lead body to prevent lateral movement of the lead at thepoint of fixation to the skull. If the compression is inadvertentlyexcessive (e.g., by overtightening of the screws or by a patientpressing down on the plate), the integrity of the lead may becompromised (e.g., the conductors between the electrodes at the leaddistal end and the connector at the lead proximal end may be shorted).

The target for a depth lead 120 is usually more precise than the targetfor a cortical strip lead 130, at least in an application where thecondition is epilepsy. That is, the target for a depth lead 130 isusually a particular structure in the brain, such as the subthalamicnucleus (STN) or the cingulate gyrus. The target for a cortical striplead 130 may be somewhat more forgiving of imprecision, that is, theelectrodes on the distal end 124 of the strip lead 120 may be destinedto cover the general area on the surface of the brain where epilepticactivity is believed to be focused. Thus, it may be especiallybeneficial to limit movement of the distal end of a depth lead once ithas been placed at the target.

In part because of the need for precision and in part because the leadis being implanted into brain tissue as opposed to on a surface of it, adepth lead 120 is most often implanted using some form of stereotaxy(e.g., with a frame affixed to the patient's skull or a “frameless”version of it). Stereotactic procedures are well known and will not bedescribed herein to any great degree. Briefly, however, one commonmethod uses frame-based stereotaxis to approach a target or targetsthrough a skull hole. The patient is given a local anesthetic and arigid frame or fixation device is attached to the patient's head, andthe brain is imaged (e.g., with a CT scan). The location of thetarget(s) is calculated based on a ‘co-registration’ of the images andthe frame, fiducials or other registered points on the head. Then, thepatient is sedated for surgery, the scalp is incised, and one or moreskull holes are formed (e.g., a burr hole or a twist drill hole) in thepatient's cranium, each at a location that will allow an appropriatetrajectory to the deep brain target(s). (Depending on the size of askull hole, it may be possible to implant more than one lead using thesame hole. For example, a 14-mm diameter burr hole is large enough toaccommodate more than one 1.27 mm diameter lead.)

Referring now to FIGS. 2 and 3, part of the stereotactic equipment 200is secured to the patient's skull using a frame, a portion of which isshown as a graduated element 202 in FIG. 2, and a guide tube 204 isoriented to provide the desired trajectory. The guide tube 204 has aninner lumen of sufficient diameter to receive a cannula 304. The cannula304 is also formed as a cylinder, typically made of a metal, such asstainless steel, and has an inner lumen with a diameter sufficient toslidably receive first an inner rod (not shown) and thereafter a depthlead (the distal end 124 of a depth lead 320 is shown in FIG. 3).

The cannula 304 may be provided with a slot 306 running along its entirelength so that the cannula can be extracted from the lead body withouthaving to retract the cannula over the proximal end 330 of the lead.Thus, if the cannula 304 is slotted, the slot 306 must be dimensioned soas to allow the proximal portion of the depth lead 320 that extendsproximally of the skull hole to be separated from the cannula throughthe slot. The depth lead 320 also has an inner lumen running throughmost of the length of the lead in which a stiffening element, such as astylet, is removably disposed. (In FIG. 3, a stylet 302 is shownextending proximally of the depth lead 320). The stylet 302 may have aplastic member or stylet handle 303 at its proximal end that the surgeoncan grab to more easily extract the stylet from the lead inner lumen.

One or more stop gauges may be configured so that they can encircle theproximal portion of either or both of the cannula 304 or the depth lead320 to guard against advancing the distal end of the cannula or thedepth lead beyond the target (not shown in FIG. 2 or 3). For example,the depth lead 320 may be measured in the operating room to identify alocation on a proximal portion that, once the lead is being routed tothe target, the surgeon can use to gauge when the lead has been advancedfar enough (or to some not-to-exceed distance) into the tissue. Thislocation on the proximal portion can be demarcated by fitting a stopgauge 310 around the lead body.

Manipulating the appropriate controls on the stereotactic equipment, thecannula 304 with the inner rod ((not shown) in place is advanced intothe brain. The inner rod discourages brain tissue from backing up intothe cannula lumen as the cannula creates a path to the target for thelead. When the cannula 304 is advanced as far as intended, the surgeonwithdraws the inner rod, and replaces it with the depth lead 320, byinserting the distal end 324 of the depth lead (with the stylet 302 inplace) into the proximal end 312 (or top) of the cannula.

FIG. 3 shows a cannula 304 with a depth lead 320 inserted within thecannula inner lumen. A proximal portion 328 of the depth lead 320extends proximally of a proximal end 312 of the cannula 304, and adistal portion 322 of the depth lead extends distally of a distal end308 of the cannula 304. The stylet 302 is disposed in an inner lumen ofthe depth lead 320 and traverses substantially the full length of thedepth lead 320, except for the very distal end 324 thereof. The stylet302 is shown extending proximally of the proximal end 129 of the depthlead 320, with a stylet handle 303 at the proximal tip. The stylet 302lends sufficient stiffness to the lead 320 while it is being manipulatedduring the implant procedure (e.g., to insert it into the cannula lumen,or in the case of a cortical strip lead, while it is being routed to thetarget by manipulating it under the skull and under the dura mater). Thestylet handle 303 makes it easier to remove the stylet 302 from the lead320 before the procedure is over. It will be appreciated that in atypical stereotactic procedure, even when the depth lead 320 is insertedinto the cannula 304 and after the lead distal end 324 has beendelivered to the target, there is enough excess lead length so that aportion of the lead body will extend proximally of the proximal end 312of the cannula, so that the lead at a point on the proximal portion 328thereof can be grasped above the proximal end 312 of the cannula 304.

After the step in the procedure where the surgeon has the distal end ofthe lead where he or she wants it, it is undesirable for subsequentsteps to move the distal end away from the target. But preventing thatfrom happening can be challenging.

First, the cannula has to be withdrawn from the brain and extracted fromaround the lead in order to complete the procedure. When a stereotacticframe is being used, the lead body extending above the proximal end ofthe cannula may be held against the inner lumen of the guide tube withthe lead oriented so that, while the cannula is slowly retracted fromthe patient, the lead can be separated from the cannula through theslot. At this point, the lead cannot be stabilized any closer to thesurface of the skull, because the cannula is in the way. During the stepof retracting the cannula, as soon as enough room is created between thedistal end of the cannula and the skull hole for the surgeon to graspthe lead body, the surgeon can use fingers, or forceps or another toolto stabilize the lead there, until the cannula is completely separatedfrom the lead. However, until the cannula clears the skull, when thelead is only being stabilized at a point in the inner lumen of the guidetube, there is a greater likelihood that the distal end of the lead willbe dislodged from the target than if the lead could be secured at ornear the skull hole.

Second, after the cannula is removed, the stylet in the inner lumen ofthe lead still has to be extracted from the lead body before theprocedure is complete. The force applied in pulling out the stylet maytend to retract the distal end of the lead along with it, so removingthe stylet is another step which may result in dislodging the lead awayfrom the target.

Third, some form of lead fixation accessory typically is used to securea proximal portion of the implanted lead at or near the skull hole orotherwise somewhere on the surface of the skull, to discourage relativemovement between the implanted distal portion of the lead and theproximal portion of the lead after the procedure is complete. The stepis another opportunity for unwanted displacement of the distal end ofthe lead from the target.

With reference to FIGS. 4A-4F, and FIGS. 9A-9G, described areembodiments of a lead fixation accessory 402 that allows a lead body tobe secured in a skull hole or on a surface of the skull proximal of askull hole while a stiffening member (e.g., a stylet) is still in thelead.

With reference to FIGS. 5A-5X, described are embodiments of a tool forstabilizing a proximal portion of a brain lead after it has beenimplanted at a target in a patient but before the lead has been securedat either the skull hole or the skull surface, to discourage relativemovement of the lead between the target and the skull.

With reference to FIG. 6 and FIGS. 7A-7R, described are methods forusing both the lead fixation accessory of FIGS. 4A-4E and the leadstabilization tool of FIGS. 5A-5H in a procedure to implant a brainlead.

With reference to FIG. 11 and FIGS. 12A-12D, described are methods forusing the lead fixation accessory of FIGS. 9A-9G in a procedure toimplant a brain lead.

Lead Fixation Accessories

A lead fixation accessory according to embodiments includes two armsthat are configured to pivot around a common point, so that they can beoriented first in an open position around a skull hole to avoidobstructing access to the skull hole before a lead is implantedtherethrough and second in a closed position so that the lead body canbe secured relative to the skull hole once the surgeon has delivered thelead to a target. When in the closed position, respective portions,e.g., edges, of the two arms engage the lead body strongly enough todiscourage relative movement of the lead between the skull hole anddistally of the skull hole (i.e., the portion of the lead that isimplanted in the patient), but not so strongly to impede any stiffeningmember disposed within an inner lumen of the lead body from movinglongitudinally within the lumen, so that the stiffening memberultimately can be removed from the lead body. Described below areexample configurations of lead fixation accessories that embody theforegoing design features.

With reference to FIGS. 4A-4I, a lead fixation accessory 402 includestwo substantially identical arms, a first arm 404 and a second arm 406.The first arm 404 has a first end 408 with a first aperture 410, asecond end 412 with a second aperture 414, and a middle region 416 thatextends between the first end and the second end. Likewise, the secondarm 406 has a first end 418 with a first aperture 420, a second end 422with a second aperture 424, and a middle region 426 that extends betweenthe first end and the second end.

With reference to FIG. 4F, in one configuration, each of the first arm404 and second arm 406 comprises two pieces—a core structure 405, 407that forms the majority of the arm, and a bumper 428, 430 in the middleregion 416, 426 of the arm. The bumper 428, 430 may surround, eithercompletely or partially, the middle region 416 of the first arm and themiddle region 426 of the second arm. The core structure 405, 407 may beformed of a first material having a first stiffness or hardness and thebumper 428, 430 may be formed of a second material having a secondstiffness or hardness that is less than the stiffness or hardness of thefirst material. For example, the first material forming the corestructures 405, 407 may be a biocompatible metal or alloy, such asstainless steel (e.g., 304SS), platinum,nickel-cobalt-chromium-molybdenum alloy (e.g., MP35N) or Nitinol, andthe second material forming the bumpers 428, 430 may be a biocompatiblepolymer, e.g. 30A-80A silicone, or biocompatible plastic, e.g.,polyurethane. In some embodiments, the second material forming thebumpers 428, is softer or more pliable than a silicone lead body, toprovide a soft plastic/silicone-to-plastic/silicone contact interfacebetween the accessory and the lead. This may result in a less abrasivelead-to-lead-fixation-accessory interface than is available with someother options for lead fixation accessories, such as a metal dog bonecranial plate.

Moreover, in one variation, the bumpers 428, 430 may have a specifiedsmoothness to encourage engagement with the surface of the lead bodywith which they contact. For example, when silicone is very smooth, itcan become tacky especially with respect to other components made ofsilicone, and the body of brain leads are often made of silicone. A moldfor manufacturing the components of the lead fixation accessory 402 outof silicone might be specified so that the bumpers at least have asurface finish that will produce very smooth silicone for thelead-contacting surface of the bumpers, e.g., with a surface finish ofeither SPI.B3 or SPI.D1. Thus, the resulting smoothness of the siliconemay render the lead-body contacting surface of each bumper sticky ortacky with respect to a silicone lead body, encouraging the lead body toremain between the arms while the compressive force of the arms aboutthe lead body is varied as, for example, the attachment mechanisms arebeing inserted, tightened, or otherwise actuated to their finalpositions for the fully deployed lead fixation accessory 402.

In another configuration, each of the first arm 404 and second arm 406comprises a single piece formed of a biocompatible polymer, e.g. 30A-80Asilicone, or biocompatible plastic, e.g., polyurethane. In other words,the entirety of the arms 404, 406 is formed of the same material. Insome embodiments, the material forming the arms 404, 406, is softer ormore pliable than a silicone lead body, to provide a softplastic/silicone-to-plastic/silicone contact interface between theaccessory and the lead. In this variation, either the entirety of thearms 404, 406 or just the middle regions of the arms intended to engagethe lead, may have a specified smoothness to encourage engagement withthe surface of the lead body with which they contact.

The first arm 404 and the second arm 406 are configured to be coupledtogether at their respective first ends 408, 418 so that theirrespective first apertures 410, 420 overlap to define a first attachmenthole 432 of the lead fixation accessory 402. The coupling allows forrotation of the arms 404, 406 relative to each other about an axispassing through the first attachment hole 432. When the lead fixationaccessory 402 is being implanted, the major surface areas of the arms404, 406 (as opposed to the edges of the arms) are positioned generallyparallel to the surface of the skull. During rotation of an arm 404,406, the major surface area of the arm slides over the surface of theskull, while remaining generally parallel to the skull surface.

With reference to FIG. 4G, in one configuration of the lead fixationaccessory 402, coupling of the first arm 404 and the second arm 406 isprovided by an attachment mechanism 409, e.g., a bone screw or a pin,during placement of the lead fixation accessory. The first attachmenthole 432 is configured to receive the attachment mechanism 409 forattaching the lead fixation accessory 402 to the skull. During placementof the lead fixation accessory 402, the first arm 404 and the second arm406 are positioned at a placement site, e.g., skull surface, so thattheir respective first apertures 410, 420 overlap to define the firstattachment hole 432. Thereafter, a bone screw 409 is secured to theskull through the attachment hole 432 to thereby couple the first arm404 and the second arm 406. To allow for rotation of the arms 404, 406,the screw 409 may be partially screwed into the skull but not screwedinto the skull so tightly that the first arm 404 and the second arm 406cannot move relative to each other.

With reference to FIGS. 4H and 4I, in other configurations of the leadfixation accessory 402, coupling of the first arm 404 and the second arm406 is provided by a hinge mechanism 411, 413 that fixedly attaches therespective first ends 408, 418 of the arms together. The hinge mechanism411, 413 is configured to allow for rotation of the arms 404, 406relative to each other about an axis passing through the hingemechanism. In the configuration shown in FIG. 4H, the hinge mechanism411 (illustrated as transparent to allow for visibility of the firstends 408, 418 of the arms) comprises a retainer having opposed faces 413a, 413 b separated by a distance 415 that allows for reception of thefirst ends 408, 418 of the arms. Each respective face 413 a, 413 bincludes an annular projection 417 a, 417 b having a size and profilethat mates with the profile of annular grooves surrounding the firstapertures 410, 420. The space between the opposed annular projection 417a, 417 b provide a friction fit between the first ends 408, 418 of thearms thereby holding them together, while allowing for rotation of thearms relative to each other. Openings 419 a, 419 b extend through therespective faces 413 a, 413 b of the hinge mechanism 411 and arepositioned to align with the first apertures 410, 420 of the arms tothereby provide a through hole for receiving a bone screw.

In the configuration shown in FIG. 41, the hinge mechanism 413(illustrated as transparent to allow for visibility of the first ends408, 418 of the arms) comprises a collar having opposed annular halves421 a, 421 b, each having a ring portion 423 a, 423 b and a cylindricalportion 425 a, 425 b. The cylindrical portions 425 a, 425 b are sized tofit through the first apertures 410, 420 of the arms 404, 406, while thering portions 423 a, 423 b have a profile that mates the annular groovessurrounding the first apertures 410, 420. The thickness of the wallsdefining the respective cylindrical portions 425 a, 425 b change, forexample, in a step like manner, and include features that allow for therespective cylinder portions to engage each other and snap fit together.The annular halves 421 a, 421 b have openings 427 a, 427 b that align tothereby provide a through hole for receiving a bone screw.

Returning to FIGS. 4A-4F, the lead fixation accessory 402 without anattachment mechanism in the attachment hole 432 is shown in an openposition in FIG. 4A and in a closed position in FIG. 4B. One of the arms404 is oriented on top of the other of the arms 406 such that the firstend 408 of the first arm 404 overlays the first end 418 of the secondarm 406. The first aperture 410 in the first arm 404 is lined up withthe aperture 420 in the second arm 406 to form the attachment hole 432.Coupled as such, the respective seconds ends 412, 422 of the arms 404,406 may be moved relative to each other to thereby provide an open stateof the lead fixation accessory 402, during which the respective secondends are displaced from each other, and a closed state, during which therespective second ends and the respective second apertures 414, 424 ofthe first and second arms overlap to define a second attachment hole434.

When an attachment mechanism like a bone screw is situated in theattachment hole 432 and at least partially engaged with the skull toanchor the lead fixation accessory 402 to the patient, the two arms 404,406 of the device can pivot 360° in a plane around the attachmentmechanism. Thus, before a lead is implanted in the skull hole, the twoarms 404, 406 can be attached to the skull with the attachment mechanismsecurely enough to keep them on the patient, but loosely enough to movethem out of the way of the skull hole while the lead is being deliveredto the target. This feature allows (but does not require) the leadfixation accessory to be partially attached to the skull surface beforea lead is introduced into the skull hole.

More particularly, early in the implant procedure, the lead fixationaccessory can be secured to the skull in the vicinity of the skull holein an open position, which does not impede access to the skull hole, orinterfere with other implant equipment, e.g., the stereotacticequipment, the slotted cannula, or the lead itself. Later in the implantprocedure, when only the lead (with a lead stylet inserted therein)remains at the skull hole, the lead fixation accessory is closed andaffixed to the skull with the other attachment mechanism, to secure thelead in place while allowing for removal of the stylet. The leadfixation accessory is thus beneficial in that it secures the lead inplace at the skull hole while the stylet is removed from the lead.

However, because the lead fixation accessory does not include acomponent that has to be situated in a burr hole before a lead isimplanted through the burr hole, it can also be deployed to secure alead body relative to a skull hole after the lead has been implanted.Thus, while it no doubt often will be more convenient to attach onecomponent of the two-piece lead fixation accessory after the skull holeis formed but before the procedure to implant a lead therethrough iscommenced, it will be appreciated that it also is possible to deploy thelead fixation accessory after the lead has been delivered to the target,since neither of the two pieces needs to be situated in the skull holeitself.

To allow the lead fixation accessory to be closed and secured at bothends to the skull surface, like the first attachment hole 432, thesecond attachment hole 434 is configured to receive an attachmentmechanism (not shown), e.g., a bone screw or pin, for securing the leadfixation accessory 402 to the skull at the second ends 412, 422 of thearms 404, 406 when it is in a closed position and oriented around thebody of a lead that has been implanted in a skull hole. When the surgeonhas the lead body situated with the desired force between the two arms,the attachment mechanisms in both attachment holes 432, 434 can betightened down against the skull to maintain the force and to compressthe lead body strongly enough to discourage the lead from pulling awayfrom the target but, if the lead has a stiffening member like a styletdisposed in an inner lumen, not so strongly as to prevent the styletfrom being withdrawn and removed from the lead.

It will be appreciated from the foregoing that the features of a giveninstance of a lead fixation accessory according to embodiments may beselected in part based on the variety of diameters of skull hole theaccessory is intended to be used with and in part on the characteristicsof the lead (s) the lead fixation accessory will be securing (e.g.,whether the lead has a removably stiffening member, the material fromwhich the lead body is formed, how and where the electrical conduits forany electrodes are situated in the lead, etc.).

FIG. 4B and 4C illustrate the lead fixation accessory 402 in a closedposition (attachment mechanisms and lead not shown). In this position,the first arm 404 and the second arm 406 form an elongated opening 436having a length 438 and a width 440. The length 438 generallycorresponds to the length of the middle region 416 of the first arm andthe middle region 426 of the second arm. The width 440 generallycorresponds to a distance between an inner edge 442 of the middle region416 of the first arm 404 and an inner edge 444 of the middle region 426of the second arm 406. The width should be selected so that when the twoarms are closed around a lead body, the lead body can be held securelywithin the lead fixation accessory 402 when the attachment mechanismsare inserted into the respective attachment holes 432, 434, but not sosecurely as to compress the lead body overmuch to (1) prevent withdrawalof any stiffening member or (2) compromise the integrity of the lead(e.g., electrical connections for electrodes).

Thus, the width defined by the inner edges 442 and 444 will depend onthe nature of the lead the lead fixation accessory 402 is intended to beused with, for example, on the outer diameter of the lead, whether ithas any inner lumens, and how much it can be compressed withoutpreventing removal of a stylet or compromising the lead integrity. Forexample, brain leads may have a diameter of only 1.27 mm, and an innerlumen in which a stylet is slidably disposed. It would be undesirable toclose the lead fixation accessory 402 around the lead with enough forceto impede movement of the stylet within the inner lumen. The smallestwidth between the two arms when the lead fixation accessory is in aclosed position may be specified to discourage that scenario.

Other brain leads provide the conductors that allow each electrode atthe distal end of the lead to be in electrical communication with aconnector at the proximal end of the lead in a coil that surrounds theinner lumen for the stylet. (For a lead design having a stylet innerlumen surrounded by a conducted coil, see, e.g., U.S. Pat. No. 7,146,222to Boling et al for Reinforced Sensing and Stimulation Leads and Use inDetection Systems). If the lead fixation accessory is intended for usewith this type of lead, the smallest width between the two arms in aclosed position may be specified to permit even less compression of thelead body, so that the integrity of the coil surrounding the styletlumen is not compromised. For example, for a 1.27 mm diameter lead witha stylet inner lumen surrounded by a coil, the recommendation may be toavoid chronically compressing the lead body more than 20%, such as whensecuring the lead at a skull hole. In this case, the lead fixationaccessory 402 may be specified so that the minimum width between the twoarms 404, 406 when the accessory is in a closed position is riot lessthan 1.02 mm (or 20% of 1.27 mm).

In specifying the dimensions of the lead fixation accessory, forexample, the length of the arms, the dimensions can be varied so thatthe accessory has a small footprint and a low profile (above the skullsurface when installed), but nevertheless can be used with a widevariety of diameters of skull hole. A limiting factor may be the largestdiameter skull hole with which the accessory is intended for use, suchthat each arm must be at least as long as the largest diameter skullhole with enough extra length to allow the arms to be affixed to theskull on either side of the skull hole. Of course, the lead fixationaccessory can be manufactured in different sizes, to permit use withdifferent maximum skull hole diameters. In one embodiment, because mostdepth lead implant procedures involve either of a 14-mm bun hole or a3.2 mm twist hole, the lead fixation accessory is designed so that thelength 438 of the middle regions 416, 426 of the first and second arms404, 406 is greater than 14 mm, such as 16.5 mm. Of course, anothervariation may be intended for use with twist drill holes of less than 5mm diameter, in which case, the length 438 may be more on the order of5.7 mm.

Further, the first arm 404 and the second arm 406 of the lead fixationaccessory 402 may be dimensioned so that the overall length 452 of theaccessory places each of the first and second attachment holes 432, 434a sufficient distance from the edge of the skull hole so that skullsurface is beneath the attachment holes when the device is centered overthe skull hole. This design ensures that any attachment mechanism used,such as bone screws, inserted through the attachment holes 432, 434, maybe fully engaged with the skull and will not overlap with the skullhole. For example, in a particular configuration of the lead fixationaccessory where the length 438 of the middle region 416 is approximately16.5 mm, the overall length 452 of the lead fixation accessory 402 isapproximately 29 mm.

The lead fixation accessory 402 may be designed to have a lower profile,relative to other known lead fixation devices, that renders theaccessory less noticeable by touch and sight to the patient and others.As described above, after a lead is implanted through a skull hole, aportion of the lead extends proximally of the skull hole, for example,until the proximal end of the lead is connected to another implanteddevice, such as the neurostimulator implanted in a tray in the skulldescribed above with reference to FIG. 1A. When a chronic connection ofthe proximal end of the lead is intended, the scalp is usually replacedto cover the skull hole and any portion of the lead extending proximallyof the lead on the skull. The patient often can feel the lead andsometimes the skull hole with a finger even after the scalp is replacedover the skull. It is generally undesirable for the patient to fiddlewith the skull hole or the proximally extending lead under the scalp,because doing so might dislodge the lead from the target or compromisethe connection at the proximal end of the lead. So, generally the lowerprofile the lead fixation accessory can be the better.

A lead fixation accessory 402 according to embodiments will extend abovethe patient's skull to some degree, by the height of the stacked firstends 408, 418 and the stacked second ends 412,422, the height of anyattachment mechanism (e.g., the head of a bone screw), and the height ofthe lead just proximal of the lead fixation accessory 402. But otherknown lead fixation accessories present an even higher profile when thedevice is installed and secured with a lead. For example, some burr holecovers are designed such that a portion of the cover extends above thesurface of a skull after implant. The more the burr hole cover extendsabove the skull surface the more the patient is likely to be annoyed bythe burr hole cover, to fiddle with it, and to be self-conscious abouthow it affects their appearance. The lead fixation accessory disclosedherein avoids these disadvantages of the known burr hole covers in thatit is designed to have a lower profile that is less noticeable to thepatient and others, and is thus more comfortable and aestheticallypleasing.

In addition, when the lead fixation accessory is used with asmaller-diameter twist drill hole, the arms 404, 406 will cover most ifnot all of the skull hole. When a lead fixation plate such as thecranial plate 154 shown in FIG. 1A is used, the lead is secured to theside of the skull hole, leaving the hole open except for the leadextending out of it. The patient may be able to feel the hole, and mayfidget with it, perhaps moving the lead around, and pushing it furtherinto the hole. The lead fixation accessory disclosed herein reduces thelikelihood that a lead will be abused in this way insofar as theaccessory at least partially covers the skull hole and thus provides aphysical barrier between the scalp and the skull hole. Thus, a patientmay be less likely to fiddle with the skull hole if the lead fixationaccessory according to embodiments is disposed over the twist drill holeinstead of to the side of it.

For a low profile, the lead fixation accessory 402 may be designed tohave a maximum height 446 between a top surface 448 (of first arm 404 inFIG. 4D) and a bottom surface 450 (of second arm 406 in FIG. 4D) that isless than the distance from the top of a typical burr hole cover to theskull surface. For example, some burr hole covers are configured suchthat the top surface of the cover lies between approximately 0.1 mm and0.2 mm above the skull surface. Accordingly, in one design of the leadfixation accessory 402, the maximum height 446 of the lead fixationaccessory 402 is less than 0.1 mm, and in one particular configurationis 0.084 mm.

A lead fixation accessory according to embodiments that is dimensionedto traverse the diameter of a burr hole (usually ≥5 mm, typically 14 mm)will also traverse the smaller diameter of a twist drill hole (usually<5 mm, typically 3.2 mm). In addition, no component of the lead fixationaccessory need be installed in or at the skull hole before the procedureto implant a lead has begun (although it may be convenient to anchor theaccessory at one of the two attachment holes 432, 434 with an attachmentmechanism beforehand, so it is ready to be manipulated into a closedposition once the lead has been delivered to the target). Further, andalthough it is anticipated that most of the time, the lead fixationaccessory will be used to traverse a skull hole, it may be used to theside of a skull hole, as with the cranial plate 154 shown in FIG. 1A.For example, if the lead is a cortical strip lead type and the holethrough which the lead is implanted is the craniectomy in which a tray112 and neurostimulator 110 are later situated, then the surgeon maywant to anchor the proximal portion of the lead to the skull between thecraniectomy and the point where the lead is connected to the connector114 of the neurostimulator. The surgeon could adjust the lead fixationaccessory 402 at an angle so that it could accommodate the lead body andattach to the skull with attachment mechanisms through the attachmentholes 432, 434, even if the arms 404, 406 are not traversing a skullhole. Thus, a lead fixation accessory according to embodiments can beadapted to secure leads of different types in different positions on theskull relative to skull holes of different diameters to achieve thefunction of discouraging movement of the lead away from the target.

With reference to FIGS. 9A-9E, in another embodiment, a lead fixationaccessory 402 for securing a lead to a skull includes a first arm 404and a second arm 406. Each of the first arm 404 and second arm 406 maybe formed of a biocompatible polymer, e.g. 30A-80A silicone, orbiocompatible plastic, e.g., polyurethane or polyetheretherketone(PEEK). The first arm 404 has a first end 408, a second end 412 havingan engagement feature 906, and a middle region 416 that extends betweenthe first end and the second end. The middle region 416 includes one ormore apertures 902 sized to receive an attachment mechanism, e.g., bonescrew, that is configured to penetrate the surface of the skull tosecure the first arm to the skull. The second arm 406 also has a firstend 418, a second end 422 having an engagement feature 908, and a middleregion 426 that extends between the first end and the second end. Themiddle region 426 of the second arm may or may not include one or moreapertures 902 sized to receive an attachment mechanism to secure thesecond arm to the skull. Each of the first arm 404 and the second arm406 is characterized by a thickness T and a surface area. When the leadfixation accessory 402 is implanted, the surface areas of the arms 404,406 are positioned generally parallel to the surface of the skull. Thesurface area may be generally send-circular in shape, as shown in FIGS.9A-9E, or may be any other geometric shape.

The first arm 404 and the second arm 406 are coupled together at theirrespective first ends 408, 418 by a coupling mechanism 904, such as ahinge pin. Coupling provided by the hinge pin 904 allows the respectivesecond ends 412, 422 of the arms 404, 406 to be moved relative to eachother to thereby provide an open position or state of the lead fixationaccessory 402 (shown in FIGS. 9A and 9E) and a closed position or stateof the lead fixation accessory (shown in FIGS. 9B-9D). During movementof an arm 404, 406, the surface area of the arm slides over the surfaceof the skull, while remaining generally parallel to the skull surface.While in an open position, the respective second ends 412, 422 aredisplaced from each other. In a closed position or state, the respectivesecond ends of the first and second arms are mechanically coupledtogether by engagement of their respective engagement features 906, 908,and the respective middle regions 416, 426 of the arms form an opening436 sized to secure the lead in place. In one configuration, theengagement features may include a detent 908 and a detent port 906 sizedto mate with the detent.

Regarding the opening 436, each of the middle regions 416, 426 includesan inner edge 442, 444, having a contour feature that defines a geometryof the opening 436. For example, the inner edge 442 of the first arm 404has an arcuate cutout 910, while the inner edge 444 of the second arm islinear and devoid of any cutouts. Configured as such, the inner edges442, 444 form an opening 436 having a semicircular geometry when thelead fixation accessory 402 is in a closed position. Many othergeometries are possible, for example, each of the inner edges 442, 444may have an arcuate cutout to form an opening having a circulargeometry, or a rectangular cutout to form a rectangular opening.Furthermore, an inner edge 442, 444 may have more than one cutout 910 toform more than one opening 436.

With reference to FIG. 9B, the opening 436 has a dimension Dcorresponding to a distance between the inner edges 442, 444 that definethe opening. The dimension is designed to provide an interference fitbetween the inner edges 442, 444 and a lead, sufficient to secure thelead in place without damaging the lead. The dimension may be describedin various ways depending on the geometry of the opening 436. Forexample, the dimension may be described as a radius (in case of asemicircular geometry), a diameter (in case of a circular geometry), ora width (in case of a rectangular geometry).

Referring to FIG. 9D, the lead fixation accessory 402 may include achannel or groove 912 sized to receive and hold in place, a portion ofthe lead body. The channel 912 is located relative to an upper surface914 of the lead fixation accessory 402 and may, for example, be formedin the second arm 406 so that it extends from the inner edge 444 of thesecond arm to a point at or near an outer edge 916 of the second arm.Alternatively, a channel may be formed in the first arm 404.Furthermore, the lead fixation accessory may include a plurality ofchannels formed in one or both of the arms 404, 406.

The channel 912 provides several beneficial features, including a meansto secure the lead in place as the lead body transitions over thesurface of the lead fixation accessory 402 from the opening 436 to theouter edge 916. The channel 912 also reduces the combined profile of thelead fixation accessory and lead body at the placement site. Morespecifically, without the channel 912 the lead body would rest on theupper surface 914 of the lead fixation accessory. Thus, the combinedprofile of the accessory and lead body would be equal to the thickness Tof the second arm 406 and the diameter (or thickness or height) of thelead body. For a lead fixation accessory 402 with a channel 912, all ora part of the diameter of the lead body would rest within the channeland the combined profile would be reduced by the depth D of the channel.This lower combined profile of the lead fixation accessory 402 and leadbody provides a placement site that is less noticeable to the patientand others, and is thus more comfortable and aesthetically pleasing.

With reference to FIG. 9E, the lead fixation accessory 402 may includestrain relief member 918 having a lead recess channel 920 sized toreceive and hold in place, a portion of the lead body, and to relievestress in the lead body. The rationale for providing strain relief to alead is illustrated in FIGS. 10A and 10B, which shows idealizedscenarios for understanding the impact of strain relief. The situationwhere a lead is firmly affixed at a given point and without a strainrelief member, is shown in FIG. 10A. When a tensile force F is appliedto a lead 1002, the helical coil structure 1004 within the lead bodyexpands uniformly except at the point of retention 1006. At the point ofretention 1006, where the lead 1002 is constrained, the force diagram1008 shows an abrupt increase in tensile force. As a result, there willbe an asymmetric distortion in the ability of the helical coil structure1004 within the lead body to flex at the last free coil 1010 that willproduce a significant stress concentration factor at the point ofretention 1006.

The situation where a lead is firmly affixed at a given point and with astrain relief member, is shown in FIG. 10B. When a tensile force F isapplied to a lead 1002, the helical coil structure 1004 within the leadbody expands uniformly up until the strain relief member 1012. Along thelength of L of the strain relief member 1012, the force diagram 1014shows a gradual change in tensile force the results in a reduced tensileforce at the fixation point 1006—relative to that shown on FIG. 10A.This reduction in tensile force will lower the stress concentrationfactor at the fixation point 1006 and reduce the probability of leadfracture

Returning to FIG. 9E, the stain relief member 918 may be formed of aflexible silicone rubber and may be associated with either of the arms404, 406. In FIG. 9E, the strain relief member 918 is associated withthe second arm 406 and may be attached, for example, by adhesion, to theupper surface 914 of the second arm. In another configuration, a strainrelief member may be integrated with, e.g., formed together with and aspart of, the second arm. An example of this configuration is shown inFIGS. 9F and 9G, which are described further below.

The stain relief member 918 includes a base portion 922 and an arcuateportion 924 that extends from the base portion. The arcuate portion 924of the strain relief member 918 provides improved strain relief overstrain relief members that are entirely straight. This is so because aforce applied to a lead at a point proximal where the lead exits thearcuate portion 924, in any vector direction relative to the arcuateportion, will induce some bending in the arcuate portion of the strainrelief member. The bending of the arcuate portion 924 reduces the forceat the base portion 922 of the strain relief member 918 and thus thestress concentration at the point where the lead enters the strainrelief member from the skull hole. For a strain relief member that isentirely straight strain, a force applied to a lead at a point proximalwhere the lead exits, in a vector direction along the length of thestrain relief member, would be less effective in reducing the stressconcentration at the point where the lead enters the strain reliefmember from the skull hole.

With reference to FIGS. 9F and 9G, in another embodiment, a leadfixation accessory 402 for securing a lead to a skull includes a firstarm 404 and a second arm 406. Each of the first arm 404 and second arm406 may be formed of a biocompatible polymer, e.g. 30A-80A silicone, orbiocompatible plastic, e.g., polyurethane or polyetheretherketone(PEEK). The first arm 404 has a first end 408 with an engagement feature926, a second end 412 with an engagement feature 928, and a middleregion 416 that extends between the first end and the second end. Themiddle region 416 includes one or more apertures 902 sized to receive anattachment mechanism, e.g., bone screw, that is configured to penetratethe surface of the skull to secure the first arm to the skull. Thesecond arm 406 also has a first end 418 with an attachment feature 930,a second end 422 with an engagement feature 932, and a middle region 426that extends between the first end and the second end. The middle region426 of the second arm may or may not include one or more apertures sizedto receive an attachment mechanism to secure the second arm to theskull. The second arm 406 further includes a strain relief member 918having a curved configuration that provides the same benefits of leadcoil strain relief described above with reference to FIG. 9E.

The respective engagement features 926, 928 of the first arm 404 and theengagement features 930, 932 of the second arm 406 combine to form acoupling mechanism by which the first and second arms connect. In theconfiguration shown in FIGS. 9F and 9G, the engagement features 926, 928of the first arm 404 are voids and the engagement features 930, 932 ofthe second arm 406 are tabs configured to mate with the voids to therebyinterlock the first and second arms.

When interlocked, the respective middle regions 416, 426 of the armsform an opening 436 sized to secure the lead in place. Like theconfigurations shown in FIGS. 9A-9E, each of the middle regions 416, 426includes an inner edge 442, 444, having a contour feature that defines ageometry of the opening 436. For example, the inner edge 442 of thefirst arm 404 has an arcuate cutout 910, while the inner edge 444 of thesecond arm is linear and devoid of any cutouts. Configured as such, theinner edges 442, 444 form an opening 436 having a semicircular geometrywhen the lead fixation accessory 402 is in a closed position. Many othergeometries are possible, for example, each of the inner edges 442, 444may have an arcuate cutout to form an opening having a circulargeometry, or a rectangular cutout to form a rectangular opening.Furthermore, an inner edge 442, 444 may have more than one cutout 910 toform more than one opening 436.

The lead fixation accessory 402 includes a channel or groove 912 sizedto receive and hold in place, a portion of the lead body. The channel912 is located relative to an upper surface 914 of the lead fixationaccessory 402 and may, for example, be formed in the second arm 406 sothat it extends from the inner edge 444 of the second arm to a point ator near the end 934 of the strain relief member 918. As previouslydescribed, the channel 912 provides several beneficial features,including a means to secure the lead in place as the lead bodytransitions over the surface of the lead fixation accessory 402. Thechannel 912 also reduces the combined profile of the lead fixationaccessory and lead body at the placement site.

Lead Stabilization Tools

FIGS. 5A-5H illustrate an embodiment of a lead stabilization tool 502for use when implanting a depth lead through a skull hole. The leadstabilization tool 502 is configured to allow the user to grasp the leadbody at or about the level of the skull hole once the distal end of thelead has been delivered to the target, to discourage dislodging the leaddistal end from the target while any remaining steps of the procedureare attended to that require handling the portion of the lead extendingproximally of the skull hole. A curved portion or hook of the tool isdimensioned to be small enough so that it can be manipulated in thespace between the inner lumen of a slotted cannula and the lead bodyoccupying the cannula to partially encircle the lead body, and then thetool applies tension to the hook so that it holds the lead stablerelative to the tool. The surgeon can then extract the lead from thecannula and/or secure the lead with a lead fixation accessory at thelevel of the skull, with less concern that these actions will pull thedistal end of the lead away from the target. Once the surgeon deems therisk that the lead will become dislodged from the target to be low, heor she can release the lead body from the tool.

To accomplish its intended functions, the lead stabilization tool 502 isconfigured to transition between three states: 1) a deactivated orresting state, 2) an extended state in which a curved, lead-grippingmember is extended, and 3) a partially retracted state in which thecurved, lead-gripping member (partially encircling the lead body) ispartially retracted into the tool housing to apply tension to the leadto hold the lead in place. An embodiment of the lead stabilization toolis shown in the deactivated or resting state in FIGS. 5A-5D, in theextended state in FIGS. 5E and 5F, and in the partially retracted staterelative to a lead body in FIGS. 5G and 5H.

As described further below in a description of an implant procedure, thetool is oriented relatively perpendicularly to a longitudinally-extendedslot in the cannula and the lead disposed therein. The tool is actuatedto the extended state to advance a member with a hook portion to aposition between the lead body and the cannula inner wall to engage thelead body. The surgeon can adjust the angle of the tool relative to thelead until confident that the hook is partially encircling the leadbody. When satisfied with the orientation of the hook relative to thelead body, the surgeon can operate the tool to partially retract themember with the hook, thus maintaining some tension between the hook andthe lead to stabilize the two elements relative to each other. Thesurgeon can maintain the tension by keeping the tool in the partiallyretracted state until other steps requiring manipulation of the leadportion extending proximally of the skull hole have been completed(e.g., separating the lead from the cannula, withdrawing the stylet fromthe lead, securing the lead in or near the skull hole with a leadfixation accessory, etc.) When those steps are completed., the surgeoncan re-extend the hook to disengage it from the lead body. Theembodiment of the lead stabilization tool 502 shown in FIGS. 5A-5H issized and configured for single-handed- and single-finger-operation. Inone configuration, the lead stabilization tool 502 is about the size ofan automobile key fob, e.g., approximately 50 mm long and 40 mm at itswidest point, and can be operated using a single button.

The lead stabilization tool 502 includes a housing 504 having a proximalend 506 and a distal end 508. The housing may be formed of a materialsuch as polycarbonate, a thermoplastic polymer such as ABS(acrylonitrile butadiene styrene) or an ABS blend, polyester, aluminum,or stainless steel. The housing 504 narrows to a nose 510 at the distalend 508. The embodiment shown in FIGS. 5A-5H is intended to bemaneuverable within the cannula relative to the lead so that a hook 534can partially encircle the lead body. Thus, the nose 510 is dimensionedso that it is not too large in any orientation relative to the slot inthe cannula to clear the edges of the slot. For example, in a particulardesign of the lead stabilization tool 502 for use with a slotted cannulahaving a slot with a width of 1.57 mm, the width 512 of the nose 510 isless than 1.57 mm. More particularly, the nose width 512 is about 1 mmless than the cannula slot width. The nose 510 may be further configuredto have a contoured or curved surface 518 having a radius of curvaturethat generally corresponds to a radius of curvature of a cylindricallead to be implanted using the cannula. As shown and described furtherbelow, this curved surface 518 provides for greater surface area contactbetween a cylindrical lead and the nose 510 during particular stages ofoperation of tool, including, for example, when a hook portion of thetool is partially retracted and pulls the lead against the nose.

Referring now to FIGS. 5D, 5E, 5G, and 5H, the housing 504 also includesa lumen 520 that extends through a portion of the housing 504 along alongitudinal axis 522. The lumen 520 terminates at an opening 524 at thedistal end 508 of the housing 504. The lead stabilization tool 502further includes an extension member 526 that is at least partiallylocated in the lumen 520. The extension member 526 is configured to bedisplaced along the longitudinal axis 522 of the housing 504. Theextension member 526 has a proximal portion or base 528 and a distalportion or grip structure 530. The grip structure 530 terminates in atip or hook 534 that is provided with a radius of curvature thatapproximates that of the brain lead types with which the tool isintended to be used. While the extension member 526 moves along thelongitudinal axis 522 when the tool is actuated between the extended andpartially withdrawn states (i.e., by pressing and releasing a pushbutton 540), the hook is always disposed outside of the housing 504.

The grip structure 530 may be formed of a metal and formed to includethe hook 534 having a radius of curvature 532. The grip structure 530may be sized to fit between the inner wall of the cannula and the leadso that the user can manipulate the hook 534 between the cannula innerwall and the lead body. For example, in a design of a lead stabilizationtool 502 for use with a cannula having an inner diameter of 1.72 mm, anda lead having a diameter of 1.27 mm, the grip structure 530 may beformed as cylinder having a diameter 536 (FIG. 5C) of approximately0.381 mm. As such, the hook 534 is able to fit easily in the spacebetween the inner wall of the cannula and the outer surface of the lead.It will be appreciated that a hook 534 with a diameter greater than thedifference in the diameters between the inner diameter of the cannulaand the outer diameter of the lead could be used, for example, to lendstrength or stiffness to the hook, since the tool can be used to pushthe lead around by the hook within the cannula. However, since anobjective is to avoid manipulating the lead so much as to dislodge thelead distal end from the target, the preferred design will be it easyfor the hook to be maneuvered into position and then maintained there,to reliably grasp the lead body.

The lead stabilization tool 502 is toggled between the deactivated orresting state, the extended state, and the partially retracted statewith an operating mechanism that is coupled to the housing 504 and tothe extension member 526. The operating mechanism includes a push button540 and a biasing mechanism. Once the tool is positioned so that thenose 510 is at or in the slot of the cannula, the user pushes the pushbutton 540, which is configured for slideable engagement with the base528 of the extension member 526. More specifically, when the tool 502 isdeactivated, the extension member 526 is fully retracted in the housing504, except for the hook 534, which remains outside the housing. Asshown in FIG. 5D, the base 528 of the extension member 526 is providedwith an angled edge 546. The push button 540 has a downward protection542 that terminates in an angled edge 544 that complements the angle ofthe angled edge 546 of the extension member. In the deactivated state,the angled edge 544 of the push button 540 rests on and matches up withthe angled edge 546 of the extension member 526. In this design,movement of the push button 540 is constrained along the vertical axis548 (FIG. 5D), i.e., up and down, using tabs 545 on the button thatcontain it in a well 551 defined proximally by a well projection 541 anddistally by wall 543 of the housing 504.

As shown in FIG. 5F, when the push button 540 is pushed, the downwardforce applied causes the angled edge 544 of the push button 540 to slidedown the angled edge 546 of the extension member 526, urging theextension member along the longitudinal axis 522 towards the nose 510.As shown in FIGS. 5E and 5F, when the push button 540 is fully engaged(i.e., pressed as far as it can be pressed), the extension member 526extends as far as the design permits outside of the housing proximal end506. In some variations, the user can apply varying pressure to thebutton to vary the degree to which the extension member extends outsideof the housing.

Transition of the lead stabilization tool 502 between the deactivatedstate (FIGS. 5A-5D) and the extended state (FIG. 5E and 5F) is aided bya biasing mechanism coupled to the push button 540 and the extensionmember 526. In the variation shown in FIGS. 5A-5H, the biasing mechanismincludes a pair of springs, one disposed at the push button 540 and theother disposed around the grip structure 530 of the extension member526. More particularly, as shown in FIGS. 5D and 5E, one of the springs560 is aligned with the push button 540 along the vertical axis 548,which is generally perpendicular to the longitudinal axis 522 alongwhich the lumen in the housing extends, and the other of the springs 562surrounds and is axially aligned with the grip structure 530 of theextension member 526 along the longitudinal axis 522.

The biasing mechanism 560, 562 has an associated biasing force thatcorresponds to an amount of force applied by the biasing mechanisms 560,562 against particular structures of the lead stabilization tool 502.The first biasing mechanism 560 applies a biasing force against the pushbutton 540, which force is sufficient to maintain the push button in thedeactivated state (FIG. 5D) when the button is not being pressed.Likewise, the second biasing mechanism 562 applies a biasing forceagainst the base 528 of the extension member 526, which force issufficient to maintain the extension member in the deactivated state(FIG. 5D) when the push button 540 is not being pressed. However, whenthe push button 540 is pressed, applying a force greater than thebiasing forces of the spring 560 at the button and the spring 562 at thegrip structure 530, the lead stabilization tool transitions to anextended state (FIG. 5E, 5F) during which the extension member 526 isdisplaced within the lumen 520 along the longitudinal axis 522 and aportion of the grip structure 530 extends out beyond the nose 510 of thetool housing 504.

FIGS. 5G and 5H are a top view and a side view of the lead stabilizationtool 502 in the third of its possible states, namely, the partiallyretracted state. Here, the hook 534 has engaged the lead body, and theuser has released the push button 540, and the biasing mechanism hascaused the extension member 526 to partially retract into the housing504. The force pulls the encircled lead up against the curved surface518 of the nose 510 and maintains the lead there, unless and until thetool is actuated again to the extended state so the lead body can bedisengaged from the hook 534.

FIGS. 5I-5M illustrate another embodiment of a lead stabilization tool550 for use when implanting a depth lead through a skull hole. In thisembodiment, the operating mechanism configured to transition the leadstabilization tool 550 between an extended state and an at leastpartially retracted state for holding a lead includes a thumb wheel 554.The thumb wheel 554 is oriented in a plan approximately perpendicular tothe plane of the extension member 552, and is configured to engage afeature of the extension member 552 when the wheel is rotated, as by anoperator's thumb or finger, to thereby move the extension member 552along the longitudinal axis 522 of the lead stabilization tool 550.

In one configuration (shown in FIGS. 5J and 5K), the thumb wheel 554 ischaracterized by a threaded portion (not visible) on an inner diameterof a thumb wheel cylinder 556 having threads which are configured tomate with a threaded portion 558 on an outer diameter of a base portion559 of the extension member 552. When the thumb wheel 554 is rotated inthe direction of the arrow 547, the threaded engagement between thethumb wheel cylinder 556 and the base portion 559 of the extensionmember 552 cause the hook 534 to extend distally. In this extendedstate, the hook 534 may be maneuvered through the slot 306 in thecannula 304 and between an inner wall of the cannula and the lead 320,to partially encircle a lead body, in the same manner as described abovewith reference to the lead stabilization tool of FIGS. 5A-5H. When thethumb wheel 554 is rotated in the direction of the arrow 549 thethreaded engagement between the thumb wheel cylinder 556 and the baseportion 559 of the extension member 552 cause the hook 534 to withdrawdistally. In this partially retracted state, the hook 534 may pull thelead body captured by the hook against the curved surface 518 of thehousing nose 510, in the same mariner as described above with referenceto the lead stabilization tool of FIGS. 5A-5H.

In another configuration, (shown in FIGS. 5L and 5M), the thumb wheel554 is characterized by a shaft 570 having a cam-coupling 572 at itsdistal end that is configured to couple with a cam-coupling 574 of theextension member 552. The cam-coupling 574 is formed as part of a baseportion 576 of the extension member 552. The shaft 570 and cam-coupling572 are fixed to the thumb wheel 554 so that rotation of the thumb wheelresults is corresponding rotation of the cam-coupling. The thumb wheel554 is coupled to the lead stabilization tool 550 housing in a way thatallows rotation of the thumb wheel about the longitudinal axis 522 ofthe tool while preventing movement of the wheel along the longitudinalaxis. A wire like portion 578 of the extension member 552 extends fromthe base portion 576 through a lumen of the shaft 570. The base portion576 includes anti-rotation features 580 that mate with correspondingfeatures (not shown) of the lead stabilization tool 550 housing in a waythat prevents rotation of the base portion 576 and cam-coupling 574about the longitudinal axis 522 of the tool while allowing movement ofit along the longitudinal axis.

When the thumb wheel 554 is rotated in the direction opposite of thearrow 582, the coupling between the cam-coupling 572 of the thumb wheeland the cam-coupling 574 of the extension member 552 assume the closedarrangement shown in FIG. 5L. This causes the base portion 576, togetherwith the rest of the extension member 552, to move in the distaldirection 586 to cause the hook 534 to extend distally. In this extendedstate, the hook 534 may be maneuvered through the slot 306 in thecannula 304 and between an inner wall of the cannula and the lead 320,to partially encircle a lead body, in the same manner as described abovewith reference to the lead stabilization tool of FIGS. 5A-5H. When thethumb wheel 554 is rotated in the direction of the arrow 582, thecoupling between the cam-coupling 572 of the thumb wheel and thecam-coupling 574 of the extension member 552 assume the open arrangementshown in FIG. M. This causes the base portion 576, together with therest of the extension member 552, to move in the proximal direction 584to cause the hook 534 to withdraw distally. In this partially retractedstate, the hook 534 may pull the lead body captured by the hook againstthe curved surface 518 of the housing nose 510, in the same manner asdescribed above with reference to the lead stabilization tool of FIGS.5A-5H.

FIG. 5N illustrates another embodiment of a lead stabilization tool 590for use when implanting a depth lead through a skull hole. In thisembodiment, the operating mechanism configured to transition the leadstabilization tool 590 between an extended state and an at leastpartially retracted state for holding a lead includes a slide button592. The slide button 592 is oriented for movement back 594 and forth596 along the longitudinal axis 522 of the lead stabilization tool 590,and is coupled to a base portion 598 of the extension member 552. Whenthe slide button 592 is operated, as by an operator's thumb or finger,the extension member 552 moves along the longitudinal axis 522 of thelead stabilization tool 590.

When the slide button 592 is moved in the direction of the arrow 596,the coupling between the slide button and the extension member 552causes the extension member 552, to move in the distal direction 586 tocause the hook 534 to extend distally. In this extended state, the hook534 may be maneuvered through the slot 306 in the cannula 304 andbetween an inner wall of the cannula and the lead 320, to partiallyencircle a lead body, in the same manner as described above withreference to the lead stabilization tool of FIGS. 5A-5H. When the slidebutton 592 is moved in the direction of the arrow 594, the couplingbetween the slide button and the extension member 552 causes theextension member to move in the proximal direction 584 to cause the hook534 to extend withdraw proximally. In this partially retracted state,the hook 534 may pull the lead body captured by the hook against thecurved surface 518 of the housing nose 510, in the same manner asdescribed above with reference to the lead stabilization tool of FIGS.5A-5H.

FIG. 5O illustrates another embodiment of a lead stabilization tool 591for use when implanting a depth lead through a skull hole. In thisembodiment, the grip structure is in the form of a slotted tube 581 thatextends from the distal end of the housing of the lead stabilizationtool 591. The slotted tube 581 includes a pair of pinchers 583 at ornear the distal end 585 of the tube that are separated by a separationdistance 587. The extension member comprises a mandrel 595 configured toslide back and forth within the slotted tube 581. The operatingmechanism configured to transition the lead stabilization tool 591between an extended state and an at least partially retracted state forholding a lead includes a slide button 593 coupled to the mandrel 595.The slide button 593 is oriented for movement back 594 and forth 596along the longitudinal axis 522 of the lead stabilization tool 591. Whenthe slide button 593 is operated, as by an operator's thumb or finger,the mandrel 595 moves along the longitudinal axis 522 of the leadstabilization tool 590.

When the slide button 593 is in a neutral position, the mandrel 595positioned away from the distal end 585 of the slotted tube 581 and theseparation distance 587 between the pinchers 583 allows for the pinchersto be maneuvered through the slot 306 in the cannula 304.

When the slide button 593 is moved in the direction of the arrow 596,the coupling between the slide button and the mandrel 595 causes themandrel to move in the distal direction 586 through the slotted tube581. The inner diameter of the slotted tube 581 reduces in size alongthe length of the tube from a proximal-end diameter to a distal-enddiameter that is smaller than the proximal-end diameter. The outerdiameter of the mandrel 595 is sized so that the mandrel slidesrelatively freely, with little interference from the slotted tube 581,as it moves through the proximal end of the tube. As the mandrel 595slides through the distal region of the slotted tube 581, there isincreased interference with the slotted tube. As a result, the mandrel595 applies radially outward force to the inside of the slotted tube 581that causes the slot 589 to expand and the separation distance 587between the pinchers 583 to increase to a size so that allows the leadbody to be positioned between the pinchers.

After the lead body is positioned between the pinchers 583, the slidebutton 593 is moved in the direction of arrow 594 to move the mandrel595 away from the distal end 585 of the slotted tube 581. Doing socauses the slot 589 to narrow and the separation distance between thepinchers 583 to decrease to a size so that lead body is held in placebetween the pinchers.

FIGS. 5P-5S illustrates alternate structures for gripping a lead thatmay be used in placed of the hook shown in FIGS. 5A-5N. These alternatestructures 561, referred to as “pincher” structures, include a pair ofarms 563, 565 coupled together at respective first ends and spaced apartat respective second ends by a distance D less than the width of theslot 306 of a cannula 304. The pincher structure 561 is attached to thedistal end of an extension member 552 and may be moved in the distaldirection and proximal direction using any of the operating mechanismsdescribed above with reference to FIGS. 5A-5N.

The distal portion of the pincher structure 561, including the coupledend of the arms 563, 565, is configured to be moved to differentpositions relative to a feature of the nose 510 of the leadstabilization tool so that the separation distance D between the armsmay be changed. The nose feature may be in the form of a cutout at thedistal end of the nose 510. In a first position of the pincher structure561 (shown in FIGS. 5P and 5R), which corresponds to an extended stateof the tool, the separation distance D between the arms 563, 565 allowsfor the arms to be maneuvered to be on either side of a lead 320. In asecond position of the pincher structure 561 (shown in FIG. 5Q and 5S),which corresponds to a partially retracted state of the tool, thepincher structure 561 is moved in the distal direction 586 such that aportion of the structure is pulled within the nose 510. This causes thearms 563, 565 to mechanically engage with the cutout feature of the nose510 and bend toward each other, which in turn, causes the separationdistance D between the arms to decrease to a size so that the lead 320is held or compressed in place between the arms.

FIGS. 5T and 5U illustrate an alternate configuration of a pincherstructure that may be used in conjunction with a pull wire. Thisalternate structure includes a pair of arms 567, 569 extending from thenose 510 of the lead stabilization tool. One of the arms 567 is coupledto a pull wire 571 which may be configured to be moved in the distaldirection and proximal direction using any of the operating mechanismsdescribed above with reference to FIGS. 5A-5N. The arm 567 is configuredto bend upon application of a pulling force through the pull wire 571.

As shown in FIG. 5T, when the pull wire 571 is in a resting state orun-pulled state, the arm 567 coupled to the pull arm assumes an unbentconfiguration and the respective arms 567, 569 are spaced apart atrespective ends by a distance D that allows for the arms to bemaneuvered to be on either side of a lead 320. As shown in FIG. 5S, whenthe pull wire 571 is in a pulled state, the arm 567 coupled to the pullarm assumes a bent configuration and the respective arms 567, 569 heldor compressed the lead 320 in place.

FIGS. 5V-5X illustrate another embodiment of a lead stabilization tool501 for use when implanting a depth lead through a skull hole. In thisembodiment, the grip structure 530 may be a distal region of theextension member 526 that is configured to transition between a linearshape and a curved shape. For example, the grip structure 530 may beformed by cutting a number of spaced apart, partial-circumference slots503 into a tubular distal region 505 of the extension member.

The operating mechanism configured to transition the lead stabilizationtool 501 between an extended state and an at least partially retractedstate for holding a lead includes two activation mechanisms, one forcontrolling the extension and retraction of the extension member 526relative to the nose 510 of the tool, and the other for controlling theshape of the grip structure 530. In the example configuration of FIGS.5V-5X, a thumb wheel 554 may be coupled to the extension member 526 tocontrol extension and retraction of the extension member, as describedabove with reference to FIG. 5I-5K. Alternatively, the extension member526 may be controlled by a push button (as shown in FIG. 5A-5H) or aslide button (as shown in FIGS. 5N and 5O) instead of a thumb wheel,

Continuing with the example of FIGS. 5V-5X, a slide button 507 controlsthe state of the grip structure 530. To this end, the operatingmechanism further includes a core wire 509 coupled to the slide button507 that extends through a lumen of the extension member 526.Alternatively, the core wire 509 may be coupled to a push button (asshown in FIG. 5A-5H) or a thumb wheel (as shown in FIG. 5I-5K) insteadof a slide button. The core wire 509 is mechanically coupled at itsproximal end 511 to the slide button 507, and at its distal end 513 tothe distal end of the grip structure 530, and s configured to slidewithin the lumen in the extension member 526.

In this embodiment of the lead stabilization tool 501, there are twostages of an extended state. In the first stage, the thumb wheel 554 isactivated to extend the extension member 526 through the nose 510 of thelead stabilization tool 501, as shown in FIG. 5W. Next, the slide button507 is moved in the distal direction 586 to move the core wire 509 inthe distal direction. Movement of the core wire 509 in the distaldirection 586 results in the application of a bending force F at thedistal end of the slotted grip structure 530, which causes the gripstructure to bend and assume the curved shape 515 shown in FIG. 5W. Thegrip structure 530 may then be maneuvered to at least partially encirclea lead.

Next, the thumb wheel 554 is operated to move the extension member 526in the proximal direction 584 to thereby retract part of the extensionmember into the nose 510 and place the lead stabilization tool 501 in apartially retracted state. Retraction of the extension member 526 pullsthe encircled lead up against the curved surface 518 of the nose 510 andmaintains the lead there, unless and until the grip structure 530assumes its linear shape 517 through movement of the slide button 507 inthe proximal direction 584, or until the tool is placed in the extendedstate (as shown in FIG. 5W) through operation of the thumb wheel 554that moves the extension member 526 in the proximal direction so thelead is no longer compressed between the nose 510 and the grip structure530.

Depth Lead implant Procedures

FIG. 6 is a flowchart of a method of implanting a depth lead through askull hole using both the lead stabilization tool of FIGS. 5A-5H and thelead fixation accessory of FIGS. 4A-4I. FIGS. 7A-7R are correspondingtop-view/side-view schematics of various stages of the method of FIG. 6.For example, FIG. 7A and FIG. 7B represent a top view (FIG. 7A) and aside view (FIG. 7B) of a particular stage of the implant procedure,while FIG. 7C and FIG. 7D represent a top view (FIG. 7C) and a side view(FIG. 7D) of another stage of the implant procedure. For clarity ofillustration, some items shown in a particular top view may not be shownin the corresponding side view. For example, the lead fixation accessory402 shown in the top view of FIG. 7C is not shown in the correspondingside view of FIG. 7D. FIG. 8 is a schematic illustration of a patient'scranium showing an implanted depth lead 320 and an implanted corticallead 802, each of which is secured at a respective skull hole 804, 806by two different lead fixation accessories 402. While the implantprocedure to be described involves the use of standard stereotacticequipment (such as shown in FIG. 2), for clarity of illustration onlythe cannula is shown in any of FIGS. 7A-7R.

In a method according to embodiments, a patient is readied for surgeryto implant a depth lead. If a stereotactic frame will be used to guidethe lead to a target 712, the frame is attached to the patient, anynecessary imaging for co-registration is undertaken, the surgeonidentifies and marks the location of a skull hole through which the leadwill be implanted, swings any stereotactic equipment obstructing accessto the patient out of the way, and incises the scalp and then forms theskull hole 710 using an air-powered drill for a standard burr hole (suchas with a 14 mm diameter) or a twist drill (such as with a 3.2 mmdiameter). (FIG. 6 at block 602 and. FIGS. 7A-7B)

While there is no stereotactic equipment in the way, and/or before anyinstruments or devices are introduced into the skull hole 710, thesurgeon may elect to attach off to one side of the skull hole one end ofa lead fixation accessory 402 such as by orienting a first arm 404 ontop of a second arm 406 of the accessory so that the respective firstapertures 410, 420 align to form a first attachment hole 432, and theninserting a bone screw or pin 702 into the hole to secure to the skullsurface 706. (FIG. 6 at block 604, FIGS. 4A-4F, and FIGS. 7A-7B). Inconfigurations of the lead fixation accessory 402 where the first arm404 and the second arm 406 are coupled together by a hinge mechanism411, 413, the end of the accessory having the hinge mechanism is securedto the skull surface 706 by inserting a bone screw into the hole 419a/419 b, 427 a/427 b extending through the hinge mechanism. (FIG. 6 atblock 604, FIGS. 4H-4I, and FIGS. 7A-7B).

After the lead is implanted, all that will be left to do to secure thelead in the lead fixation accessory 402 will be to close the two arms404, 406 around the lead extending proximally of the skull hole 710,line up the two arms so that the respective second apertures 414, 424form a second attachment hole 434, insert another bone screw or pin intothe hole, and tighten down both attachment mechanisms until the leadfixation assembly is secure against the lead body and the skull surface.Alternatively, the surgeon can wait until after the lead has beendelivered to the target to use the lead fixation accessory, since nopart of the lead fixation accessory must be secured in or near the skullhole before the lead is introduced into the skull hole 710.

Before the depth lead is introduced to the patient, it can be measuredto mark a point on a proximal portion of the lead that corresponds tothe distance from the skull to the target plus the distance from theskull to the top of the cannula, so that when the lead has been advancedthrough the cannula far enough for the marked point to reach the top ofthe cannula, the surgeon will know the lead has been implanted farenough. A stop gauge 310 may he placed around the diameter of the depthlead on a proximal portion of the depth lead at a point calculated toprovide feedback to the surgeon that the distal lead end has reached thetarget when the point coincides with the proximal end of the cannuladuring implantation of the lead (i.e., a cue as to when to stopadvancing the lead) (FIG. 6 at block 606).

Next, the stereotactic equipment is readied for use with the lead. If aframe is being used, a slotted cannula 304 is inserted into a guide tube(see the guide tube 204 in FIG. 2) at a trajectory relative to the skullhole 710 that is designed to reach the target 712. The cannula 304 mayhave an inner rod (riot shown) slidably disposed therein to discouragetissue from backing up into the interior of the cannula as it is used tocreate a path for the depth lead. The surgeon advances the cannula 304so that the distal end 308 of the cannula 304 is at or near the target712 (FIG. 6 at block 608 and FIGS. 7C-7D).

Next, the surgeon introduces the distal end 324 of the depth lead 320into the cannula lumen at the top of the cannula the proximal end 312 ofthe cannula 304). The surgeon advances the depth lead 320 through thecannula until the distal end 324 of the depth lead is at the target 712(FIG. 6 at 610). If a stop gauge 310 has been placed on the proximalportion 328 of the depth lead, then the surgeon will be cued that thedistal end 324 has reached the target 712 when the stop gauge reachesthe proximal end 312. (FIG. 6, block 610 and FIGS. 7E-7F),

Once the surgeon is satisfied that the distal end 324 of the lead 320 isat the target 712, he or she wants to stabilize the lead near the skullhole 710 while subsequent steps that require manipulation of the portionof the lead 328 extending proximally of the skull hole are attended to.Thus, in FIG. 6 at blocks 612, 614, 616, 618, and 620, and FIGS. 7G-7P),a lead stabilization tool 502 is used to secure the lead while theproximal portion 328 of the lead 320 is still within the cannula 304,since extracting the lead from the cannula is a step that requiresmanipulation of the proximal portion 328 of the lead 320.

Next, with the tool 502 in the deactivated or resting state, the surgeonbrings the nose 510 of the housing with the hook 534 extending slightlytherefrom adjacent the cannula slot 736 or inside the slot. (FIG. 6 atblock 612 and FIGS. 7G-7H). Then the surgeon presses the push button 540to extend the hook 534, and maneuvers the extended hook within the spacebetween the cannula 304 inner wall and the lead 320 to partiallyencircle the lead body with the hook. (FIG. 6 at blocks 616, and FIGS.7I-7J). When the surgeon is confident that the hook 534 will engage thelead 320, he or she releases the push button 540, which exerts a forcethat pulls the hook back towards the tool housing 504, and partiallywithdraws the extended hook until the lead body is secured between thehook and the nose 510 of the housing. (FIG. 6 at block 618, and FIGS.7K-7L).

Next, the surgeon withdraws the slotted cannula 304 from the skull hole710. Then, the proximal lead portion 328 is extracted through thecannula slot 736 until it is entirely free of the cannula 304. While thelead 320 and the cannula 304 are being separated, the lead stabilizationtool 502 is maintained in the partially retracted state to hold the leadsecurely against the tool to stabilize it and minimize movement of thedistal portion 322 of the lead 320. (FIG. 6 at block 620, and FIGS.7M-7N).

Next, while the lead stabilization tool 502 is still maintained in thepartially retracted state to hold the lead 320 in place, the surgeonundertakes steps to secure the lead to the skull surface 706 by, movingthe first arm 404 and the second arm 406 of the lead fixation accessory402 relative to each other to place the lead fixation accessory 402 in aclosed position around the lead 320, with a second end of the leadfixation accessory 402 at a second side 716 of the skull hole 710opposite the first side 708 of the skull hole. The second end of thelead fixation accessory 402 is then secured to the skull surface 706 byslightly rotating the tool 502 as necessary to gain access to the secondattachment hole 434 formed at the second end of the lead fixationaccessory, and inserting a screw (not visible) through the hole tothereby maintain the lead fixation accessory 402 in a locked positionand secure the portion of the lead 320 adjacent the skull hole 710 inplace while the stylet 302 is still in the lead. (FIG. 6 at block 620,and FIGS. 7O-7P).

Next, once the lead fixation accessory 402 is secured around the lead320 in the closed position, the portion of the lead being gripped by thelead stabilization tool 502 can he released from the lead stabilizationtool. To accomplish this, the surgeon presses the push button 540 toextend the hook away from the nose 510, so that the lead body is nolonger captured between the hook and the housing and can be freed fromthe lead stabilization tool 502. (FIG. 6 at block 622, and FIGS. 7Q-7R).

Next, the stylet 302 is removed from the lead 320. (FIG. 6 at block 624,and FIGS. 7Q-7R). As previously described with reference to FIGS. 4A-4F,the lead fixation accessory 402 is configured to secure the lead 320 inplace through a compressive force. While the compressive force issufficient to secure the lead in place, the force is great enough toimpede removal of the stylet 302 from the lead 320. Accordingly, if thesurgeon prefers, the stylet 302 may be removed prior to releasing thelead 320 from the lead stabilization tool 502. For example,style(removal may occur along with other steps in block 620.

Upon securing the lead fixation accessory 402 in the closed position,the distal end 324 of the lead 320 is discouraged from movingappreciably relative to the proximal portion 328 of the lead thatextends from the lead fixation accessory 402, even when the proximalportion is manipulated, for example, when the surgeon attaches aproximal end to another device internally or externally of the patientor when the patient fiddles or fusses with the proximal portion afterimplant.

FIG. 11 is a flowchart of a method of implanting a depth lead through askull hole using a lead fixation accessory of FIGS. 9A-9G. FIGS. 12A-12Dare corresponding schematics of various stages of the method of FIG. 11.The method of FIG. 11 may also employ the lead stabilization tool ofFIGS. 5A-5H.

In a method according to embodiments, a patient is readied for surgeryto implant a depth lead. If a stereotactic frame will be used to guidethe lead to a target site, the frame is attached to the patient, anynecessary imaging for co-registration is undertaken, the surgeonidentifies and marks the location of a skull hole 1202 through which thedepth lead will be implanted, swings any stereotactic equipmentobstructing access to the patient out of the way, and incises the scalpand then forms the skull hole 1202 through the skull 1204 using a twistdrill (such as with a 3.2 mm diameter). (FIG. 11 at block 1102 and FIG.12A).

Next, while there is no stereotactic equipment in the way, and/or beforeany instruments or devices are introduced into the skull hole 1202, thesurgeon places a lead fixation accessory 402 at the implant site. Tothis end, the lead fixation accessory 402 is placed in a closedposition, such as shown in FIG. 9B, and positioned over the skull hole1202. The surgeon visually aligns the opening 436 of the lead fixationaccessory 402 with the skull hole 1202 and inserts an alignment pin 1206through the opening and into the skull hole to establish properalignment of the opening and skull hole. An attachment mechanism 1208,e.g., bone screw, is secured to the skull 1204 through an aperture 902.(FIG. 11 at block 1104, FIG. 9B, and FIG. 12B).

Next, the alignment pin 1206 is removed from the lead fixation accessory402. The lead fixation accessory 402 is then placed in an open position,such as shown in FIG. 9A, to allow access to the skull hole 1202 forpurposes of implanting a depth lead at the target site. Proceduressimilar to those described above with respect to blocks 604-618 of FIG.6 may be performed to implant the lead at the target. (FIG. 11 at block1106)

Next, after the distal end 324 of the depth lead 320 is placed at thetarget site, the lead fixation accessory 402 is placed in a closedposition, as shown in FIGS. 12C and 12D, to secure the lead in place. Ifthe configuration of the lead fixation accessory 402 has additionalapertures 902, such as shown in FIG. 9C, one or more bones screws may beused to further secure the accessory to the skull. If a stylet 302 isused to place the lead 320 and is still installed within the lead, thestylet is then removed. (FIG. 11 at block 1108 and FIG. 12C). Next, theproximal portion 328 of the lead is positioned. For example, if theconfiguration of the lead fixation accessory 402 includes a channel 912(as shown in FIG. 9D) or a strain relief 918 with a channel 920 (asshown in FIG. 9E), the proximal portion 328 of the lead 320 may beplaced in the channel. (FIG. 11 at block 1110 and FIG. 12D).

The various aspects of this disclosure are provided to enable one ofordinary skill in the art to practice the present invention. Variousmodifications to exemplary embodiments presented throughout thisdisclosure will be readily apparent to those skilled in the art. Thus,the claims are not intended to be limited to the various aspects of thisdisclosure, but are to be accorded the full scope consistent with thelanguage of the claims. All structural and functional equivalents to thevarious components of the exemplary embodiments described throughoutthis disclosure that are known or later come to be known to those ofordinary skill in the art are expressly incorporated herein by referenceand are intended to be encompassed by the claims. Moreover, nothingdisclosed herein is intended to be dedicated to the public regardless ofwhether such disclosure is explicitly recited in the claims. No claimelement is to be construed under the provisions of 35 U.S.C. § 112,sixth paragraph, unless the element is expressly recited using thephrase “means for” or, in the case of a method claim, the element isrecited using the phrase “step for.”

What is claimed is:
 1. A lead stabilization tool for holding a lead inplace near a hole in a skull, while the lead is positioned in a cannulapassing through the hole, the cannula having a slotted wall having awidth, the lead stabilization tool comprising: a housing having aproximal end, a nose at a distal end, and a lumen extending at leastpartially through the housing along a longitudinal axis of the housing,the lumen defining an opening through the nose of the housing; anextension member at least partially located in the housing andconfigured for displacement along the longitudinal axis; a gripstructure configured to fit through the slotted wall of the cannula; andan operating mechanism coupled to the housing and at least one of theextension member and the grip structure, and configured to transitionthe lead stabilization tool between: 1) an extended state during whichthe grip structure is located distal the nose and can be positionedthrough the slotted wall and manipulated to at least partially encirclethe lead, and 2) an at least partially retracted state during which thegrip structure is located relative to the nose so as to apply a force tothe lead to thereby hold the lead in place.
 2. The lead stabilizationtool of claim 1, wherein the nose at the distal end of the housing isconfigured to fit through the slotted wall of the cannula.
 3. The leadstabilization tool of claim 1, wherein the extension member comprises adistal region and the grip structure is associated with the distalregion.
 4. The lead stabilization tool of claim 3, wherein the gripstructure comprises a hook formed at the distal end of the extensionmember.
 5. The lead stabilization tool of claim 4, wherein the lead hasa cylindrical lead body having a radius of curvature, and the hook has aradius of curvature generally corresponding to the radius of curvatureof the cylindrical lead body.
 6. The lead stabilization tool of claim 3,wherein the grip structure comprises a pincher at the distal end of theextension member, comprising at least two arms coupled together atrespective first ends and spaced apart at respective second ends by adistance less than the width of the slotted wall.
 7. The leadstabilization tool of claim 3, wherein the grip structure comprises adistal region of the extension member configured to transition from asubstantially linear shape to a curved shape through an application offorce by a core wire extending from the operating mechanism to an end ofthe distal region of the extension member.
 8. The lead stabilizationtool of claim 1, wherein the operating mechanism comprises a push buttonconfigured for slideable engagement with a base of the extension member.9. The lead stabilization tool of claim 8, wherein the operatingmechanism further comprises: a biasing mechanism coupled to the pushbutton and the extension member, the biasing mechanism configured to, inan absence of an application of a force greater than a biasing force ofthe biasing mechanism, maintain the lead stabilization tool in the atleast partially retracted, and wherein the push button is configured toreceive a force and, upon receiving a force greater than the biasingforce of the biasing mechanism, to transition the lead stabilizationtool to the extended state.
 10. The lead stabilization tool of claim 9,wherein the biasing mechanism comprises: a first biasing memberassociated with the push button; and a second biasing member associatedwith the extension member.
 11. The lead stabilization tool of claim 10,wherein the second biasing member is axially aligned with thelongitudinal axis of the housing, and the first biasing member isaxially aligned with an axis generally perpendicular to the longitudinalaxis.
 12. The lead stabilization tool of claim 1, wherein the operatingmechanism comprises a thumb wheel configured for rotational engagementwith a base of the extension member.
 13. The lead stabilization tool ofclaim 12, wherein the operating mechanism further comprises: a threadedportion of the thumb wheel; and a threaded portion of the base of theextension member engaged with the threaded portion of the thumb wheel,wherein the thumb wheel is configured to receive a rotational force in afirst direction which transfers to the base of the extension member andcauses the lead stabilization tool to transition to the extended state,and to receive a rotational force in a second direction which transfersto the base of the extension member and causes the lead stabilizationtool to transition to the at least partially retracted state.
 14. Thelead stabilization tool of claim 1, wherein the operating mechanismcomprises a slide button fixedly coupled to a base of the extensionmember.
 15. The lead stabilization tool of claim 14, wherein the slidebutton is configured to receive a force in a first direction along thelongitudinal axis which transfers to the base of the extension memberand causes the lead stabilization tool to transition to the extendedstate, and to receive a force in a second direction along thelongitudinal axis which transfers to the base of the extension memberand causes the lead stabilization tool to transition to the at leastpartially retracted state.
 16. The lead stabilization tool of claim 1,wherein: the grip structure comprises a slotted tube extending from thenose and a pair of pinchers at or near a distal end of the slotted tube,and the extension member comprises a mandrel configured to slide backand forth within the slotted tube to thereby decrease and increase aseparation distance between the pair of pinchers.